1. Field of the Invention
The invention relates to a method of localizing an object in a turbid medium, which method includes the following steps: immersing the turbid medium in a calibration medium, irradiating the turbid medium, measuring intensities of a part of the light transported through the turbid medium and the calibration medium along a plurality of light paths, normalizing the measured intensities and reconstructing an image of the interior of the turbid medium from the normalized intensities. The invention also relates to a device for carrying out a method of this kind.
2. Description of the Related Art
In the context of the present application the term light is to be understood to mean electromagnetic radiation of a wavelength in the range of from 400 to 1400 nm. Furthermore, a turbid medium is to be understood to mean a substance consisting of a material having a high light scattering coefficient. Examples in this respect are an Intralipid solution or biological tissue. Furthermore, attenuation coefficient is to be understood to mean the inverse diffuse absorption distance K which is given as , K=3.mu..sub.a +L .mu.'.sub.s +L in which .mu.'.sub.s is the reduced scatter coefficient and .mu..sub.a is the absorption coefficient.
A method of this kind is described in patent application EP 97202187.7. The known method can be used for in vivo breast examinations to determine the presence of tumors in breast tissue of a human or animal female. In order to counteract edge effects, according to the known method an attenuation coefficient of the calibration medium is made equal to a predetermined mean attenuation coefficient of the breast tissue. This can be achieved, for example by choosing a calibration medium in the form of a liquid with a solution of, for example Intralipid, having an attenuation coefficient which is equal to the predetermined mean attenuation coefficient of the breast tissue. Another possibility is to add a dye to the liquid with the dissolved Intralipid with a predetermined fixed percentage, and to detune the wavelength of the light to be generated by the light source in such a manner that the attenuation coefficient of the calibration medium is equal to the predetermined mean attenuation coefficient of the breast tissue. Furthermore, in order to prevent artefacts in the reconstructed image which are due to transitions between the calibration medium and an environment of the calibration medium, the measured intensities are normalized.
It is a drawback of the known method that an actual mean attenuation coefficient of the breast tissue of the body to be examined varies relative to the predetermined mean attenuation coefficient. This is due, for example to the fact that a mean attenuation coefficient of breast tissue of a group of females of approximately the same age is taken for the value of the predetermined mean attenuation coefficient. Consequently, artifacts are liable to occur in the reconstructed image of the interior of the breast.